The suite gates the change
A language change that fails the suite is refused. The refusal is the same shape as every other refusal in this site.
Testing a compiler
A compiler is tested with pairs of source and answer. The pairs are a file, and the file is the contract of the language so far.
What you will see
change allowed. A failing pair would refuse, which is the gate.
About 1 min of reading
Try It
Write the contract file
1
Write a good pair
printf 'src=1+2 want=3\n' > /tmp/p.txt; cat /tmp/p.txt
Before you run it, say out loud what it will print. Then open the answer.
What it prints
One line with both sides. Both sides written is the claim.
2
Write a bad pair
printf 'src=1+ want=place:2\n' >> /tmp/p.txt; wc -l < /tmp/p.txt
Before you run it, say out loud what it will print. Then open the answer.
What it prints
2. The bad case is in the same file, which is the contract.
3
Run the suite and gate
printf 'fail=0\n' | awk '{print ($1=="fail=0") ? "change allowed" : "change refused"}'
Before you run it, say out loud what it will print. Then open the answer.
What it prints
change allowed. A failing pair would refuse, which is the gate.
Data Flow
A pair to a gate
1
The pair is written with both sides
↓
2
The bad pairs are written in the same file
↓
3
Every pair runs
↓
4
A failing pair refuses the change
Why this works
When you have a choice
Why the tree is compared rather than the answer
Two trees can give one answer. Comparing the tree compares the meaning, which is the stronger claim.
Examples
The pair is source to answer
Both sides are written. A test with both sides written is a test that cannot be talked around.
The bad pairs are in the same file
A pair that expects a place is a pair like any other. The bad cases are part of the contract, not apart from it.
The file is the suite
Every pair runs. A suite that is a file is a suite that a change to the language must pass.
Words this lesson uses
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.
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